gpio-usbdetect: Register interrupt handler after getting gpio value

Currently driver is first getting irq number and then registering
interrupt handler with kernel. After that driver is getting gpio value
from dts. If interrupt gets fired right after interrupt handler
registration, it could lead to XPU violation as gpio value is zero, whose
TLMM register might not have access from kernel.

Change-Id: Iff864c1263f45ab6ed58238532e5003716732a99
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>