drivers/leds/leds-lp5521.c: check if reset is successful

drivers/leds/leds-lp5521.c: check if reset is successful

Make sure that the reset is successful by issuing a dummy read to R
channel current register and check its default value.  On some platforms,
without this dummy read, any further access to {R/G/B}_EXEC will not have
any impact.

[[email protected]: fix up code comment]
Signed-off-by: srinidhi kasagar <[email protected]>
Tested-by: Naga Radhesh <[email protected]>
Acked-by: Linus Walleij <[email protected]>
Cc: Richard Purdie <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>