spi: cadence: Change usleep_range() to udelay(), for atomic context

The path "spi: cadence: Add usleep_range() for
cdns_spi_fill_tx_fifo()" added a usleep_range() function call,
which cannot be used in atomic context.
However the cdns_spi_fill_tx_fifo() function can be called during
an interrupt which may result in a kernel panic:

BUG: scheduling while atomic: grep/561/0x00010002
Modules linked in:
Preemption disabled at:
[<ffffff800858ea28>] wait_for_common+0x48/0x178
CPU: 0 PID: 561 Comm: grep Not tainted 4.17.0 #1
Hardware name: Cadence CSP (DT)
Call trace:
 dump_backtrace+0x0/0x198
 show_stack+0x14/0x20
 dump_stack+0x8c/0xac
 __schedule_bug+0x6c/0xb8
 __schedule+0x570/0x5d8
 schedule+0x34/0x98
 schedule_hrtimeout_range_clock+0x98/0x110
 schedule_hrtimeout_range+0x10/0x18
 usleep_range+0x64/0x98
 cdns_spi_fill_tx_fifo+0x70/0xb0
 cdns_spi_irq+0xd0/0xe0
 __handle_irq_event_percpu+0x9c/0x128
 handle_irq_event_percpu+0x34/0x88
 handle_irq_event+0x48/0x78
 handle_fasteoi_irq+0xbc/0x1b0
 generic_handle_irq+0x24/0x38
 __handle_domain_irq+0x84/0xf8
 gic_handle_irq+0xc4/0x180

This patch replaces the function call with udelay() which can be
used in an atomic context, like an interrupt.
Signed-off-by: Jan Kotas <jank@cadence.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org

drivers/spi/spi-cadence.c

@@ -319,7 +319,7 @@ static void cdns_spi_fill_tx_fifo(struct cdns_spi *xspi)
 		 */
 		if (cdns_spi_read(xspi, CDNS_SPI_ISR) &
 		    CDNS_SPI_IXR_TXFULL)
-			usleep_range(10, 20);
+			udelay(10);
 
 		if (xspi->txbuf)
 			cdns_spi_write(xspi, CDNS_SPI_TXD, *xspi->txbuf++);