pcie-gadget-spear: use devm_ functions

The various devm_ functions allocate memory that is released when a
driver detaches. This patch uses these functions for data that is
allocated in the probe function of a platform device and is only freed
in the remove function. Also, the unnecessary labels are removed and
linux/device.h is added to make sure the devm_*() routine declarations
are unambiguously available.

The initial call to platform_get_resource is moved down to the
introduced call to devm_ioremap_resource that uses its result.

Signed-off-by: Himangi Saraogi <himangi774@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>