If gpmc_cs_remap() fails we will get an error because we are calling
release_resource() on an uninitialized resource. Let's fix that by
checking the resource flags. And while at it, let's also make
gpmc_cs_delete_mem() use the res pointer that we already have to
avoid confusion.

Without this patch we can get the following error:

omap-gpmc 6e000000.gpmc: cannot remap GPMC CS 1 to 0x01000300
Unable to handle kernel NULL pointer dereference at virtual address 00000018
...
(gpmc_cs_free+0x94/0xc8)
(gpmc_probe_generic_child+0x178/0x1ec)
(gpmc_probe_dt+0x1bc/0x2cc)
(gpmc_probe+0x250/0x44c)
(platform_drv_probe+0x3c/0x6c)
(really_probe+0x74/0x208)
(driver_probe_device+0x34/0x50)
(bus_for_each_drv+0x60/0x8c)
(device_attach+0x80/0xa4)
(bus_probe_device+0x88/0xb0)
(device_add+0x320/0x450)
(of_platform_device_create_pdata+0x80/0x9c)
(of_platform_bus_create+0xd0/0x170)
(of_platform_bus_create+0x12c/0x170)
(of_platform_populate+0x60/0x98)
(pdata_quirks_init+0x30/0x48)
(customize_machine+0x20/0x48)
(do_one_initcall+0x2c/0x14c)
(do_basic_setup+0x98/0xd8)
(kernel_init_freeable+0x12c/0x1e0)
(kernel_init+0x8/0xf0)
(ret_from_fork+0x14/0x2c)
Code: e1a04000 e59f0070 eb195136 e5942010 (e5923018)

Cc: Pekon Gupta <pekon@ti.com>
Reviewed-by: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: tony Lindgren <tony@atomide.com>