usb: phy: qusb: Fix check to enable dpdm regulator

Commit a69fe6c4 ("usb: phy: Fix compilation errors") inverted
check for dpdm regulator enable/disable causing dpdm regulator is
never getting turned ON. This results into dpdm state not being seen
in High-Z state causing USB charger detection failure. Fix this issue
by correcting the check as well rename rm_pulldown as dpdm_enable to
reflect actual functionality.

Also fix check with dpdm regulator related enable/disable APIs with
return value of qusb_phy_enable_power() API.

Change-Id: I351222b1b3c7c47fe44599e4b213af8280d6b551
Signed-off-by: Mayank Rana <mrana@codeaurora.org>