phy: mapphone-mdm6600: add gpiolib dependency

commit 208d3423 upstream.

gcc points out that when CONFIG_GPIOLIB is disabled,
gpiod_get_array_value_cansleep() returns 0 but fails to set its output:

drivers/phy/motorola/phy-mapphone-mdm6600.c: In function 'phy_mdm6600_status':
drivers/phy/motorola/phy-mapphone-mdm6600.c:220:24: error: 'values[0]' is used uninitialized in this function [-Werror=uninitialized]

This could be fixed more generally in gpiolib by returning a failure
code, but for this specific case, the easier workaround is to add a
gpiolib dependency.

Fixes: 5d1ebbda ("phy: mapphone-mdm6600: Add USB PHY driver for MDM6600 on Droid 4")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>