USB: set device dma_mask without reference to global data

Many USB host drivers contain code such as:

if (!pdev->dev.dma_mask)
        pdev->dev.dma_mask = &tegra_ehci_dma_mask;

... where tegra_ehci_dma_mask is a global. I suspect this code originated
in commit 4a53f4e6

 "USB: ehci-tegra: add probing through device tree" and
was simply copied everywhere else.

This works fine when the code is built-in, but can cause a crash when the
code is in a module. The first module load sets up the dma_mask pointer,
but if the module is removed and re-inserted, the value is now non-NULL,
and hence is not updated to point at the new location, and hence points
at a stale location within the previous module load address, which in
turn causes a crash if the pointer is de-referenced.

The simplest way of solving this seems to be to copy the code from
ehci-platform.c, which uses the coherent_dma_mask as the target for the
dma_mask pointer.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Tony Prisk <linux@prisktech.co.nz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>