msm: pcie: clear Request Exit L1 bit when enabling L1 via debugfs

When enabling L1 via debugfs commands, the request exit L1
bit needs to be cleared so the link can enter L1.

Change-Id: I41b6d3b856473bebc1337eb467763a6f66914e41
Signed-off-by: Tony Truong <truong@codeaurora.org>