extcon: max77843: Fix signedness bug in max77843_muic_set_debounce_time()

This patch fixes the variable type of 'ret' from 'unsigned int' to 'int' type
because the return type of regmap_update_bits() is 'int' type.

Fixes: 27a28d32 ('extcon: max77843: Add max77843 MUIC driver')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
[cw00.choi: Fix the patch description]
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>