leds: fix Kconfig text for MLXCPLD, SYSCON, MC13783, NETXBIG

It fixes grammatical errors in Kconfig file for LEDS_SYSCON,
LEDS_MLXCPLD, LEDS_MC13783, LEDS_NETXBIG.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>