The 16-bit Root Capabilities register is at offset 0x1e in the PCIe
Capability. Rename current 'rsvd' struct member to 'rootcap'.

Link: https://lore.kernel.org/r/20210722144041.12661-4-pali@kernel.orgSigned-off-by: NPali Rohár <pali@kernel.org>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: NMarek Behún <kabel@kernel.org>