clocksource/drivers/fsl_ftm_timer: Fix error return checking

The error checks on freq for a negative error return always fails because
freq is unsigned and can never be negative. Fix this by making freq a
signed long.

Detected with Coccinelle:
drivers/clocksource/fsl_ftm_timer.c:287:5-9: WARNING: Unsigned expression
compared with zero: freq <= 0
drivers/clocksource/fsl_ftm_timer.c:291:5-9: WARNING: Unsigned expression
compared with zero: freq <= 0

Fixes: 2529c3a33079 ("clocksource: Add Freescale FlexTimer Module (FTM) timer support")
Signed-off-by: Colin Ian King <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Cc: Daniel Lezcano <[e-mail]>
Cc: [e-mail]
Link: https://lkml.kernel.org/r/[e-mail]

drivers/clocksource/fsl_ftm_timer.c

···
 
 static unsigned long __init ftm_clk_init(struct device_node *np)
 {
-	unsigned long freq;
+	long freq;
 
 	freq = __ftm_clk_init(np, "ftm-evt-counter-en", "ftm-evt");
 	if (freq <= 0)