ARM: keystone: Drop the un-necessary dsb from keystone_cpu_smc()

This was added because of some legacy reasons from OMAP SOCs but
after testing and verifying with the keystone hardware folks, the
dsb in keystone_cpu_smc() is not necessary.

So drop it.
Reported-by: Dave Martin <dave.martin@linaro.org>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

arch/arm/mach-keystone/smc.S

@@ -24,6 +24,5 @@
 ENTRY(keystone_cpu_smc)
 	stmfd   sp!, {r4-r11, lr}
 	smc	#0
-	dsb
 	ldmfd   sp!, {r4-r11, pc}
 ENDPROC(keystone_cpu_smc)