staging: mt7621-pci: rename 'PCIE_P2P_MAX' into 'PCIE_P2P_CNT'

staging: mt7621-pci: rename 'PCIE_P2P_MAX' into 'PCIE_P2P_CNT'

Definition 'PCIE_P2P_MAX' is '3'. The value here is not a MAXimum.
It is a count or a number. It is how many masks there are.
The masks are numbered 0, 1, 2 so the maximum is 2. Hence rename
variable into 'PCIE_P2P_CNT' which is a more accurate name.

Suggested-by: NeilBrown <neil@brown.name>
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20200413155018.31921-1-sergio.paracuellos@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>