da850evm: Use clrbits function with correct endianess

The current code uses clrbits_be32 which is incorrect since we are on
a little endian machine here. This patch fixes this issue and also removes
some unnecessary code: Reading the current GPIO bank state is not required
if we are using the SET and CLEAR GPIO registers for setting/clearing
bits.

Signed-off-by: Christian Riesch <christian.riesch@omicron.at>
Cc: Nagabhushana Netagunte <nagabhushana.netagunte@ti.com>
Cc: Rajashekhara, Sudhakar <sudhakar.raj@ti.com>