drivers/misc/apds9802als.c: fix signedness bug

i2c_smbus_read_byte_data() may return negative error code.  This is not
seen to als_sensing_range_store() as the result is stored in unsigned int.

Made it signed.

Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
Cc: Hong Liu <hong.liu@intel.com>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Anantha Narayanan <anantha.narayanan@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>