pcie-gadget-spear: fix error return code in spear_pcie_gadget_probe()

Fix to return a negative error code in the clk_get_sys() and clk_enable()
error handling case instead of 0, as done elsewhere in this function.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>