Fix system chrash caused by groups whose number is smaller than the number
of groups of the last pinctl instance which is not initialized.

iMX7D supports two iomux controllers (iomuxc-lpsr and iomuxc) on probing
the second instance (iomuxc) the chrash below occurs.

Uncompressing Linux... done, booting the kernel.
[    0.000000] Booting Linux on physical CPU 0x0
[    0.000000] Linux version 4.2.0-next-20150901-00006-gebfa43c (aalonso@bluefly)
[    0.000000] CPU: ARMv7 Processor [410fc075] revision 5 (ARMv7)
[    0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasin instruction cache
[    0.000000] Machine model: Freescale i.MX7 SabreSD Board
[    0.661012] [<802a6cb0>] (strcmp) from [<802cc80c>] (imx_dt_node_to_map+0x58/0x208)
[    0.668879] [<802cc80c>] (imx_dt_node_to_map) from [<802cbe24>] (pinctrl_dt_to_map+0x174/0x2b0)
[    0.677654] [<802cbe24>] (pinctrl_dt_to_map) from [<802c8f18>] (pinctrl_get+0x100/0x424)
[    0.685878] [<802c8f18>] (pinctrl_get) from [<802c9510>] (pinctrl_register+0x26c/0x480)
[    0.694104] [<802c9510>] (pinctrl_register) from [<802ccf3c>] (imx_pinctrl_probe+0x580/0x6e8)
[    0.702706] [<802ccf3c>] (imx_pinctrl_probe) from [<80351b58>] (platform_drv_probe+0x44/0xa4)
[    0.711455] [<80351b58>] (platform_drv_probe) from [<803503ec>] (driver_probe_device+0x174/0x2b4)
[    0.720405] [<803503ec>] (driver_probe_device) from [<803505fc>] (__driver_attach+0x8c/0x90)
[    0.728982] [<803505fc>] (__driver_attach) from [<8034e930>] (bus_for_each_dev+0x6c/0xa0)
[    0.737381] [<8034e930>] (bus_for_each_dev) from [<8034fb88>] (bus_add_driver+0x148/0x1f0)
[    0.745804] [<8034fb88>] (bus_add_driver) from [<80350c00>] (driver_register+0x78/0xf8)
[    0.753880] [<80350c00>] (driver_register) from [<800097d0>] (do_one_initcall+0x8c/0x1d4)
[    0.762282] [<800097d0>] (do_one_initcall) from [<80987dac>] (kernel_init_freeable+0x144/0x1e4)
[    0.771061] [<80987dac>] (kernel_init_freeable) from [<806d9c7c>] (kernel_init+0x8/0xe8)
[    0.779285] [<806d9c7c>] (kernel_init) from [<8000f628>] (ret_from_fork+0x14/0x2c)
[    0.786981] Code: e3520000 e5e32001 1afffffb e12fff1e (e4d03001)
Signed-off-by: Robin Gong <b38343@freescale.com>
Signed-off-by: Adrian Alonso <aalonso@freescale.com>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>