doc: watchdog: fix typos etc

Correct typos in lockup-watchdogs.rst.

Link: https://lkml.kernel.org/r/20260408213523.2707947-1-rdunlap@infradead.org
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Björn Persson <Bjorn@xn--rombobjrn-67a.se>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: rddunlap

Documentation/admin-guide/lockup-watchdogs.rst

@@ -41,15 +41,15 @@ is a trade-off between fast response to lockups and detection overhead.
 Implementation
 ==============
 
-The soft and hard lockup detectors are built around a hrtimer.
+The soft and hard lockup detectors are built around an hrtimer.
 In addition, the softlockup detector regularly schedules a job, and
 the hard lockup detector might use Perf/NMI events on architectures
 that support it.
 
 Frequency and Heartbeats
 ------------------------
 
-The core of the detectors in a hrtimer. It servers multiple purpose:
+The core of the detectors is an hrtimer. It serves multiple purposes:
 
 - schedules watchdog job for the softlockup detector
 - bumps the interrupt counter for hardlockup detectors (heartbeat)