hv_netvsc: Remove rmsg_pgcnt

hv_netvsc: Remove rmsg_pgcnt

init_page_array() now always creates a single page buffer array entry
for the rndis message, even if the rndis message crosses a page
boundary. As such, the number of page buffer array entries used for
the rndis message must no longer be tracked -- it is always just 1.
Remove the rmsg_pgcnt field and use "1" where the value is needed.

Cc: <stable@vger.kernel.org> # 6.1.x
Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Link: https://patch.msgid.link/20250513000604.1396-5-mhklinux@outlook.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>